1. Field of the Invention
This invention relates to an ink supply device and an ink jet recording apparatus having the ink supply device.
2. Related Background Art
As an ink jet recording apparatus, there has heretofore been proposed one of a structure in which an ink supply path leading from an ink supply tank through a recording head back to the ink supply tank is formed and an electromagnetic valve and a pump are interposed in the intermediate portion of this supply path and the apparatus can be set to various modes by controlling them.
An example of the recording apparatus of this type according to the prior art is shown in FIG. 1 of the accompanying drawings.
In FIG. 1 which illustrates the whole of the ink supply path, reference numeral 1 designates a plurality of head elements of the type which discharges ink, for example, by the use of heat energy. The head elements have a number of nozzles and are disposed widthwisely of recording paper.
Each of the head elements 1 has two flow paths 2 and 3, one of which 2, is connected to a distributor flow path 4 and the other flow path 3 is connected to another distributor flow path 5.
The distributor flow path 4 is connected to a first ink tank 7 through a flow path 6, and an electromagnetic valve A is disposed in the intermediate portion of the flow path 6.
The other distributor flow path 5 is connected to the first ink tank 7 through a flow path 8. An electromagnetic valve C and a pump P are disposed in the intermediate portion of the flow path 8. The pump P is driven by a reversible motor M and can change over the direction of ink supply.
A liquid level sensor 9 is mounted in the first ink tank 7 to always monitor the level of ink.
The first ink tank 7 is adapted to be capable of being opened to the atmosphere through a pipe 10 and an electromagnetic valve B disposed in the intermediate portion thereof so as to keep the pressure in the tank constant.
On the other hand, a removable mounted second ink tank 12 is connected in the intermediate portion of the flow path 8 and between an electromagnetic valve C and the pump P through a check valve 11.
The example shown in FIG. 1 is shown in a state corresponding to ink of one color, but in the case of a multi-color printer, a number of such flow path systems as described above will be provided independently by colors.
Under the construction as described above, the electromagnetic valves A-C and the pump are controlled as shown in Table 1 below in accordance with respective modes.
(1) Print Mode
In this case, the electromagnetic valves A and B are opened and the electromagnetic valve C is closed. The shown example is an on-demand type ink jet printer and therefore, during the recording, no pressure is applied to ink and accordingly, the pump P is not driven. Ink is supplied to the head elements 1 through the electromagnetic valve A, the flow path 6, the distributor flow path 4 and the flow path 2.
Also, when ink flows out of the first ink tank and the interior of the tank assumes a negative pressure, air is sucked through the electromagnetic valve B and the interior of the tank is kept at a predetermined pressure.
(2) Supply Mode
In this mode, only the electromagnetic valve C is closed and the other electromagnetic valves are opened, and the pump is revolved in a forward direction and ink is supplied from the second tank 12 to the first tank 7. This mode is applied when the printer begins to be used and when the amount of ink in the first tank 7 has decreased.
(3) Pressurization Mode
This mode is applied where pressure is applied to ink to thereby force the ink out of the nozzles of the head elements and effect ink non-discharge recovery operation when the nozzles have become dry or when the nozzles are clogged.
In this mode, only the electromagnetic valve A is closed and the other electromagnetic valves are opened and the motor is revolved in the reverse direction, and the ink from the first ink tank 7 is supplied to the head elements 1 through the flow path 8, the electromagnetic valve C, the distributor flow path 5 and the flow path 3 and discharge of the ink is effected.
(4) Circulation Mode
This mode is a mode for supplying ink to each head during the initial use of the apparatus or eliminating the bubbles in the head and flow paths by circulating the ink, and is applied where the printer is left unused for a long time.
In this case, all of the electromagnetic valves are opened and the motor is revolved in the reverse direction, and ink is supplied from the tank to the head elements 1 through the flow paths 8, 5 and 3 and returns into the tank through the flow paths 2, 4 and 6.
The bubbles in the head elements or in the flow paths are collected into the first ink tank 7 and discharged into the atmosphere through the electromagnetic valve B.
(5) Preservation Mode
This mode is a mode for preventing evaporation and degeneration of the ink in the first ink tank 7 and preventing leakage of the ink, and is used during the long-time non-use of the apparatus or during the transportation of the apparatus.
In this case, all electromagnetic valves are closed and the motor is stopped, and it does not happen that due to changes in the ambient conditions (temperature, humidity, etc.), the ink in the tank leaks from the head portion or air, dust and the like enter the supply path.
TABLE 1 ______________________________________ Valve A Valve B Valve C Pump ______________________________________ Print Open Open Close Stop Supply Open Open Close .dwnarw. Forward Pressurization Close Open Open .uparw. Reverse Circulation Open Open Open .uparw. Reverse Preservation Close Close Close Stop ______________________________________
The various modes as described above can be suitably changed over to make the apparatus display its function.
However, the adoption of the above-described structure has in some cases given rise to the following problems.
First, the flow of ink is effected under the control of the electromagnetic valves A-C and the pump and therefore, the frequency of change-over of the magnetic valves and the frequency of stoppage and reversal of revolution of the pump are high, and this complicates the hardware and software of the sequence control and also requires a long time for the power supply to the electromagnetic valves, which has given rise to the problems of great power consumption and great amount of heat generation.
Also, the flow of ink is controlled by the opening-closing of the electromagnetic valves and therefore, the pressure in the flow path fluctuates each time the valves are opened and closed, and in some cases this has given rise to a problem that ink leaks from the nozzles or air is absorbed to produce bubbles.
Further, the slight overflow of ink from the flow path system and the great deal of overflow caused by an accident or the like cannot be distinguished from each other, and the apparatus cannot be set to a safe state simultaneously with the occurrence of the great deal of overflow, which has also in some cases given rise to a problem that outflow of ink arises.
Generally, an overflow sensor used to detect overflow is designed to detect an excess of the level of the liquid in a container over a predetermined set amount by electrical or mechanical detecting means.
The electrical detecting means include means utilizing the short circuiting between electrodes and means utilizing a variation in electrostatic capacity caused by the amount of liquid present between electrodes, and the mechanical detecting means include a float, a mechanical switch, etc.
However, any of the conventional overflow sensors as described above could not detect the state of overflow unless the liquid level reached the level of the detecting means.
Accordingly, for example, neither the liquid supplied little by little nor the liquid supplied in a great deal due to an accident or the like could be recognized as the state of overflow unless it was detected by the detecting means.
However, for example, when a state in which a great deal of liquid is fed to the overflow sensor side is not conceivable except in the case of an accident, if the operator waits until the liquid collects in the container and the level of that liquid is detected by the detecting means, it will delay the countermeasure for the apparatus said and will thus lead to a serious accident or trouble.
Also, in an ink jet printer or the like having a removable mounted head unit, as soon as the head unit is mounted on the body side, it must be electrically connected and also mechanically connected to a flow path system which effects circulation of ink.
A valve device provided in such a connecting portion need prevent back flow of liquid such as ink even if the pressure in the flow path system on the head unit side rises, and also the valve need be opened by all means when the head unit is mounted, and the valve need be closed by all means when the head unit is removed.
On the other hand, this valve must be of an electromagnetic valve structure in order to effect electrical control when ink-non-discharge recovery operation or the like is performed.
Where an electromagnetic valve is employed, it must be closed except when the head unit is mounted and at such time, the electric current is cut off.
Accordingly, this electromagnetic valve must be of the normally closed type structure which is always closed when an electric current is not supplied thereto.
Said valve is of a structure in which the coil is energized and the valve is opened when the head unit is connected to the body side and an electric current is supplied to the valve.
The role of the valve can be performed by the structure as described above, but in such a structure, an electric current must be supplied to the electromagnetic valve whenever the head unit is mounted.
As a result, the power consumption increases and the amount of heat generation becomes great as previously noted, and wasteful energy is consumed.
A check valve used in an ink jet recording apparatus has heretofore required a great stroke in sealing and has thus suffered from an inconvenience that it slowly responds to the mounting or dismounting of a cartridge filled with liquid and the liquid leaks from the cartridge.
Also, the valve has been of a complex structure which is provided with a slot, a cross hole, etc., and thus has led to a problem of higher cost.
In addition, for example, in ink jet printer or the like has an ink flow path system leading from an ink tank to an ink jet head, and a pump, a valve, etc., for supplying ink are disposed in the ink flow path system.
In the flow path system of such a structure, there occurs water hammer attributable to the inertia of fluid such as ink when the pump is stopped from operating or when the valve is opened and closed.
When such water hammer occurs, ink may be injected or ooze, for example, out of the nozzle of the head due to the pressure of the water hammer, thereb y staining recording paper and/or the head.
To prevent the occurrence of such water hammer, there have been proposed apparatuses in which a chamber is provided in the intermediate portion of the flow path and a body of great mass is contained in the chamber so that the pressure of water hammer is converted into the kinetic energy of this body, whereby the water hammer may be absorbed, and apparatuses of a structure in which shock means such as an accumulator is provided in the flow path system.
However, any of the conventional structures as described above has been complex and unsuitable for a small-scale flow path system of a small flow rate and high in cost.
Also, for example, in a color ink jet printer or the like, use is made of a plurality of kinds of containers called cartridges filled with different colors of inks.
These containers need be replaced with new ones when the ink therein becomes exhausted, and are removably mounted with respect to the apparatus.
Also, an ink cartridge filled with a particular color of ink is adapted to be mounted at a particular position, and if that cartridge is mounted at a different position, mixing of inks will occur.
So, cut-away portions have been formed in the fore end portion of an ink cartridge at different position correspondingly to the colors of inks and projections have been provided on the apparatus side correspondingly to the respective cut-away portions so that the ink cartridge cannot be completely mounted unless the projections are coincident with the cut-away portions.
Adoption of such a structure prevents wrong mounting of the ink cartridge.
However, adoption of the structure as described above gives rise to the following problems.
First comes the problem of a metal mold.
That is, to mold containers formed with cut-away portions at different positions, a number of containers corresponding to the kinds of containers must be prepared, and this means high cost.
There is also a method which does not use different metal molds, but uses a core to mold by a signal metal mold, whereas in this case, the core is complicated and thus, the cost becomes high as in the case where a number of metal molds are used.
Another problem is the problem in custody and handling of containers.
That is, containers differ only in the positions and shapes of cut-away portions and are of entirely the same shape in the other portions and therefore, wrong selection by the operator may occur.
Still another great problem is wrong loading of ink resulting from the above-mentioned wrong selection.
That is, in the present situation, the ink loading work is carried out without involving the automatic selection of containers and therefore, if the operator commits a mistake in selecting containers, different colors of inks will be loaded into a containers and, if such containers are mounted in the printer, it may lead to a serious accident such as mixing of inks or the recording by two or more kinds of inks of the same color.